The world's demand for electric energy is continuously increasing. A vast amount of electric energy is currently generated by oil, gas, coal or nuclear plants. However, burning oil, gas and coal results in polluted air, and all of these fuel resources are rapidly diminishing. Nuclear energy requires the disposal of nuclear waste, which remains dangerous for centuries.
Natural energy sources are effectively inexhaustible and are abundantly available throughout the world in various forms such as natural wind, solar, tidal and wave energy. Unfortunately, natural energy sources have an irregular nature, and peak demands for electrical energy in homes and in industry are usually out of phase with the availability of natural sources of energy.
Wind energy conversion technology is today regarded as one of the most technically advanced technologies available that can effectively help develop a low carbon economy while ensuring a clean and secure supply of energy. However, wind is inherently variable. Some days are windy, some are not, and even during a single day wind varies throughout the day. Consequently, a mismatch frequently occurs between potential energy available from low winds during periods of peak demand, and high winds during periods when the demands of the electrical grid may be low, such as in the evening. Further, due to the nature of wind farms being located distant to cities requiring energy, at times the power generated in wind farms can exceed the capacity of the transmission lines communicating the power to the grid requiring it. Unable to transmit the power generated during peak winds, frequently wind farms will idle turbines which could be producing electrical energy at a maximum rate.
Similarly, solar energy is most abundant typically during the middle of the day, however, solar cells generate no electricity at night. Additionally, solar energy farms are frequently located at a significant distance from the power grids they serve, and transmission lines can limit the amount of power that may be transmitted from the solar power farm to the distant grid. If transmission lines lack the capacity to transmit the full amount of power of a solar power farm produced at midday, the energy will have to be shed and wasted.
Likewise, tidal and wave power does not often coincide with the times of peak electrical energy demand.
Accordingly, it is necessary that the energy obtained from natural energy sources be somehow stored so as to be releasable during periods of power demand, as required.
A variety of techniques are available to store excess power for later delivery. One approach to energy storage is the use of batteries. Large storage batteries have been developed on a commercial basis and have been used both on farms and in industry. Electrical storage batteries, however, are objectionable due to problems relating to durability and maintenance. Moreover, many large-scale batteries use a lead electrode and acid electrolyte, and these components are environmentally hazardous.
Energy can also be stored in ultracapacitors. A capacitor is charged by line current so that it stores charge, which can be discharged rapidly when needed. Appropriate power-conditioning circuits are used to convert the power into the appropriate phase and frequency of AC. However, a large array of such capacitors is needed to store a substantial amount of electrical energy. Ultracapacitors, while being more environmentally friendly and lasting longer than batteries, are substantially more expensive, and still require periodic replacement due to the breakdown of internal dielectrics, etc.
Pumped hydro and compressed air systems are known in the art. For example, U.S. Pat. No. 4,010,614 describes a system for converting natural energy into usable electricity. The system includes an elevated reservoir for the storage of excess energy. A solar collector produces steam to drive an electrical generator and a hydraulic pump. When the demand for electrical energy is below the capacity of the generator, the excess energy is used to drive the hydraulic pump. Water is transported by the hydraulic pump from a low level reservoir to the elevated reservoir to thereby store potential energy. When demand increases beyond the capacity of the generator or when the supply of solar energy is decreased sufficiently, water from the elevated reservoir is used to drive a second electrical generator.
U.S. Pat. No. 4,058,070 describes a system utilizing kinetic energy of the wind that is converted into compressed air which is stored, in the system, at a predetermined output pressure. The compressed air is used for driving a turbine coupled to an electrical power generator.
U.S. Pat. No. 4,206,608 describes an apparatus and method for utilizing natural energy in the production of electricity. The natural energy obtained from a plurality of natural energy sources is utilized to pressurize hydraulic fluid. A plurality of natural energy sources are used so that periodic and intermittent fluctuations in the supply of natural energy of one particular form may be compensated for by the other forms of natural energy. The pressurized hydraulic fluid is supplied to a pressure storage tank wherein a compressible fluid is compressed by the pressurized hydraulic fluid. Electrical energy is produced by the pressurized hydraulic fluid and is supplied as needed to various consumers. Excess electricity which is not needed by consumers is supplied to an electric motor which drives a hydraulic pump. The excess energy is thereby utilized to pressurize hydraulic fluid which is supplied to the high pressure storage tanks. In this way, excess energy is conserved and is not wasted needlessly.
U.S. Pat. No. 7,239,035 describes an integrated, wind-pumped hydro power generation system that includes at least one wind turbine generator device configured to generate output power for a common bus, and at least one hydro generator device configured to generate output power for the common bus. The hydro generator device is powered by water flow. The wind turbine generator device and the hydro generator device include corresponding local controls associated therewith, and a set of supervisory controls is in communication with the common bus and each of the local controls.
Existing commercial offshore wind farms are based on seabed-mounted foundations technology to support wind turbines that are only suited for shallow waters typically at depths usually not exceeding 50 meters. Floating offshore wind technologies enable the exploitation of untapped wind resources at deep water sites further away from the coast where marine wind energy resources are more abundant and continuous than those on shore. Moreover, issues related to visual, noise and ecological impacts, as well as potential conflicts with shipping, aviation and coastal surveillance are expected to be of a lesser concern.
For example, U.S. Pat. No. 8,169,099 describes a deep off-shore floating wind turbine apparatus and methods of manufacturing, operating, maintaining, protecting and conveying the wind turbine apparatus. The wind turbine includes a rotor converting a motion of air into a movement of the rotor, a hub housing equipment that transforms the movement of the rotor into a useful form of energy, and a tower supporting the hub on one end. The wind turbine further includes a base floating substantially at the water surface and movable with respect to the underlying solid surface. The tower is connected to the floating base on the second end. The wind turbine also includes a tilting mechanism tilting the wind turbine into a substantially horizontal orientation and bringing it back into an upright position, as well as a rotating mechanism operable to control azimuth orientation of the wind turbine.
U.S. Pat. No. 8,662,793 describes a floating wind farm that includes a plurality of floating rafts connected with one another and disposed in a body of water below the water by a predetermined distance. A plurality of wind turbines are connected to the floating rafts respectively and configured to be driven by wind and thereby generate power. A power generator is connected to the floating rafts. A plurality of anchors are connected to the floating rafts respectively and disposed in the water for confining the location of the floating rafts. Each of the floating rafts includes at least three pipes and a plurality of ballast blocks attached to the pipes. The pipes are configured to store air compressed by the power generated by the wind turbines. The power generator is configured to generate and output electricity from the compressed air stored in the pipes.